Methods, storage medium and apparatus for encoding and decoding sound signals from multiple channels

ABSTRACT

A method for encoding sound signals on multiple channels includes extracting an arbitrary number of sine waves from each of the sound signals. The sine waves include at least a first sine wave, extracted from a first one of the channels and having first-channel information, and a second sine wave, extracted from a second one of the channels and having second-channel information. Using the first-channel information and one of the second-channel information and sine wave information corresponding to a predetermined sine wave, one of the second-channel information and the sine wave information corresponding to the predetermined sine wave is selected as a to-be-correlated object for encoding in a correlation with the first-channel information. The correlation includes a frequency-based absolute value of a difference between frequency information included in the first-channel information and frequency information included in the second-channel information and is used to encode the first- and second-channel information.

BACKGROUND OF THE INVENTION

The present invention generally relates to a sound signal encodingmethod and apparatus, sound signal decoding method and apparatus,program, and a recording medium, and more particularly to a sound signalencoding method and apparatus for making high-efficiency coding of soundsignals from a plurality of channels and transmitting the encoded soundsignals or recording the signals to a recording medium, a recordingmedium having recorded therein a string of codes generated by thecoding, a sound signal decoding method and apparatus for decoding thestring of codes received or reproduced, a program for causing a computerto execute the sound signal coding or decoding process, and acomputer-readable recording medium having the program recorded therein.

This application claims the priority of the Japanese Patent ApplicationNo. 2002-145267 filed on May 20, 2002, the entirety of which isincorporated by reference herein.

Conventionally, the unblocked frequency subband techniques representedby the subband coding or the like and the blocked frequency subbandtechniques represented by the transform coding or the like are known formaking high-efficiency coding of audio signals such as sounds.

With the unblocked frequency subband techniques, a time-based audio isencoded by dividing it into a plurality of frequency subbands withoutblocking it. On the other hand, with the blocked frequency subbandcoding techniques, a time-based audio signal is divided into a pluralityof frequency subbands by making frequency spectrum transform of thesignal into a frequency-based signal, namely, coefficients obtainedthrough the frequency spectrum transform of the audio signal are groupedby each of predetermined frequency subbands, and then the signal isencoded by the frequency subbands.

For an improved efficiency of coding, there has also been proposed ahigh-efficiency encoding technique being a combination of the unblockedfrequency subband coding and blocked frequency subband coding. With thistechnique, a frequency band of a signal is divided by the subband codinginto frequency subbands, for example, then the signal of each frequencysubband is spectrally transformed into a frequency-based signal, and thesignal is encoded by the spectrally transformed frequency subbands.

For dividing a frequency band, the quadrature mirror filter (QMF), forexample, is used frequently since it can easily divide the frequencyband with cancellation of aliasing. It should be noted that thefrequency band division by the QMF is described in detail in thedocument “1976 R. E. Crochiere, Digital Coding of Speech in Subbands,Bell Syst. Tech. J. Vol. 55, No. 8, 1976” and the like.

The frequency subband techniques further include the polyphasequadrature filter (PQF), for example. This technique is to divide afrequency band into equal bandwidths. The PQF technique is detailed inthe document “ICASSP 83 BOSTON, Polyphase Quadrature Filters—A newsubband coding technique, Joseph H. Rothweiler” and the like.

On the other hand, the aforementioned frequency spectrum transformtechniques includes a one by which an input audio signal is blocked intoframes of a predetermined unit time, and a time-based signal istransformed into a frequency-based signal by subjecting each block todiscrete Fourier transform (DFT), discrete cosine transform (DCT),modified discrete cosine transform (MDCT) or the like.

Note that the MDCT is described in detail in the document “ICASSP, 1987,Subband/Transform Coding Using Filter Bank Designs Based on Time DomainAliasing Cancellation, J. P. Princen, A. B. Bradley, Univ. of SurveyRoyal Melbourne Inst. of Tech.” and the like.

By quantizing the signal of each frequency band, produced using thefilter or spectrum transform as above, it is possible to control afrequency band caused by a quantization noise, whereby the signal can beencoded with an acoustically higher efficiency with the use of themasking effect of the noise. Also, the signal can be encoded with a muchhigher efficiency by normalizing signal components of each frequencysubband with a largest absolute value of the signal components of thesubband, for example.

The width of each frequency subband is determined with the humanauditory sense, for example. Generally, an audio signal is divided intoa plurality of frequency subbands (32 subbands, for example) called“critical band” of which the width is larger as the frequency is higher.

Also, to encode data of each frequency subband, a predetermined bitallocation or an adaptive bit allocation is made to the frequencysubband. That is to say, to encode coefficient data obtained through theMDCT by a bit allocation, a number of bits are adaptively allocated toMDCT coefficient data of each frequency subband, obtained through theMDCT of each block of signal.

For configuration of an actual code string, first quantization accuracyinformation indicating a quantization step and a normalizationcoefficient indicating a coefficient used to normalize each signalcomponent are encoded with a predetermined number of bits for eachfrequency subband to be normalized and quantized, and then thenormalized and quantized spectrum signal is encoded.

For a further improvement of the compression ratio from a value, maininformation to directly be encoded, for example, it is necessary toimprove the efficiency of encoding the spectrum signal as well as theefficiency of encoding sub-information which is not encoded directlysuch as the quantization accuracy information, normalization coefficientand the like.

On this account, the Inventors of the present invention have proposed,by the specification and drawings included in the Japanese patentapplication No. 2000-390589 already fined, a technique of improving theefficiency of encoding such sub-information with a variable-lengthcoding using an inter-channel correlation between audio signals or acoding by controlling the range of existential distribution using thegradient coefficient.

Also, the Inventors of the present invention have proposed, by thespecification and drawings included in the Japanese Patent ApplicationNo. 2001-182093, a technique of improving the efficiency of encodinggain information by the use of various kinds of correlation in a codingin which a gain control is made to suppress quantization noises called“pre-echo/post-echo”, caused by the quantization of the spectrum signal.

Furthermore, the Inventors of the present invention has proposed, by thespecification and drawings included in the Japanese Patent ApplicationNos. 2000-380639 and 2001-182384, a technique of improving theefficiency of coding by a extracting tone component from a time-seriessignal and making spectrum transform coding of a residual error toprevent the efficiency of coding from being deteriorated by the tonecomponent existent in a local frequency such as a sine wave, which wasobserved in the conventional coding techniques.

Note that the sine wave information indicating the extracted tonecomponent, for example, waveform parameters such as frequencyinformation, amplitude information, phase information, are encodedseparately from the spectrum information, normalization information andquantization accuracy information of the residual error signal.

The ratio of compression can be increased by encoding the residual errorsignal with the technique disclosed in the specification and drawingsincluded in the Inventors' Japanese patent application No. 2000-390589or 2001-182093, for example the variable-length coding using aninter-channel correlation between audio signals or the coding bycontrolling the range of existential distribution using the gradientcoefficient.

Different from the spectrum information, normalization information orquantum accuracy information of the residual error signal, however, theextracted tone component exists evenly in all the frequency bands, sothat the coding efficiency will be worse in the variable-length codingusing an inter-channel correlation between audio signals as the case maybe.

The conventional variable-length coding using the inter-channelcorrelation between audio signals will be described in detail below. Inthe following description, it is assumed that the number of channels istwo (2), namely, the audio signals are stereo signals, and theinter-channel correlation means a correlation between right and leftchannels. Also, although there will be described an example in which thecorrelation between the right and left channels is used for onlyamplitude information of the sine wave information indicating a tonecomponent, the description is also true for phase information. Further,it is assumed that there have been extracted a number N.sub.L of sinewaves on the left channel Lch and a number of N.sub.R sine waves on theright channel Rch.

FIG. 1 shows the general construction of a portion of a conventionalsine wave information encoder which encodes sine wave information withthe use of a correlation between the right and left channels, thatencodes amplitude information on the right channel Rch. For thesimplicity of illustration and explanation, however, it is assumed herethat the number N_(L) of sine waves on the left channel Lch is equal tothe number N_(R) of sine waves on the right channel Rch. As shown inFIG. 1, the sine wave information encoder, generally indicated with areference number 200, includes a left-channel amplitude informationholder 201, right-channel amplitude information holder 202,adder-subtracter 203, variable-length encoder 204 and a code stringgenerator 205.

The left-channel amplitude information holder 201 indexes a number N_(L)of sine waves extracted from the left channel Lch by 0 to N_(L)−1,respectively, sequentially starting with the lowest-frequency one, andholds amplitude information in correspondence to the indexes. Similarly,the right-channel amplitude information holder 202 indexes a numberN_(R) of sine waves extracted from the right channel Rch by 0 toN_(R)−1, respectively, sequentially starting with the lowest-frequencyone, and holds amplitude information in correspondence to the indexes.Then, the left- and right-channel amplitude information holders 201 and202 supply the amplitude information held therein to theadder-subtracter 203.

The adder-subtracter 203 calculates a difference by subtracting the i-thamplitude information on the left channel Lch from the i-th amplitudeinformation on the right channel Rch, and supplies the difference thuscalculated to the variable-length encoder 204.

The variable-length encoder 204 makes variable-length coding of thedifference supplied from the adder-subtracter 203 according to avariable-length code table to provide a variable-length code, andsupplies the variable-length code as a sine wave information code to thecode string generator 205.

The code string generator 205 generates a code string according to thesine wave information code supplied from the variable-length encoder204.

When supplied with sine wave information as shown in FIG. 2, the sinewave information encoder 1 works as will be described below. As will beknown, many of the information on the right channel are similar in valueto corresponding ones on the left channel, and so the correlationbetween the right and left channels can be utilized to encode theinformation with an improved efficiency. In encoding amplitudeinformation (3 bits when not compressed), the difference resulted fromsubtraction of amplitude information on the left channel Lch from one onthe right channel Rch, corresponding in index (n) to the amplitudeinformation on the left channel Lch, will be as shown in FIG. 3. Sincethe difference distribution is not even, the number of bits encoded canbe reduced by making variable-length coding according to avariable-length code table as shown in FIG. 4 for example. Morespecifically, the amplitude information on the right channel Rch can beencoded with a total of 5 bits. Namely, the phase information (of 12bits (=3 bits×4) when not compressed) can be compressed by 7 bits.

Similarly, in encoding phase information (of 3 bits when notcompressed), the difference resulted from subtraction of phaseinformation on the left channel from that on the right channel Rch,corresponding in index (n) to the amplitude information on the leftchannel Lch, will be as shown in FIG. 5. By making variable-lengthcoding of the difference according to the variable-length code tableshown in FIG. 4, the phase information on the right channel Rch can beencoded with a total of 5 bits. This number of bits is 7 bits smallerthan 12 bits (=3 bits×4) when the phase information is not compressed.

When supplied with sine wave information as shown in FIG. 6, the sinewave information encoder 1 works as will be described below. As will beknown, many of information on the right channel are similar in value tocorresponding ones on the left channel. Since a difference is calculatedbetween the amplitude information on the right channel Rch and that onthe left channel Lch, corresponding in index (n) to the amplitudeinformation on the right channel Rch, the difference is a total of 14bits as shown in FIG. 7. The amplitude information is of 12 bits whennot compressed. Similarly, the difference in phase information betweenthe right and left channels Rch and Lch is a total of 24 bits as shownin FIG. 8, which means a lower efficiency of coding than when the phaseinformation is not compressed.

SUMMARY OF THE INVENTION

Accordingly, the present invention has an object to overcome theabove-mentioned drawbacks of the conventional techniques forhigh-efficiency coding of audio signals such as sounds or the like byproviding a novel sound signal encoding method and apparatus, arecording medium having recorded therein a code string generated by thesound signal encoding method and apparatus, a sound signal decodingmethod and apparatus for receiving or reproducing and decoding the codestring, a program for allowing a computer to perform the sound signalencoding or sound signal decoding, and a computer-readable recordingmedium having the program recorded therein.

Another object of the present invention is to provide a sound signalencoding method and apparatus, capable of encoding sound signals with animproved efficiency with a variable-length encoding technique using aninter-channel correlation between the sound signals, a recording mediumhaving recorded therein a code string generated by the sound signalencoding method and apparatus, a sound signal decoding method andapparatus for receiving or reproducing and decoding the code string, aprogram for allowing a computer to perform the sound signal encoding orsound signal decoding, and a computer-readable recording medium havingthe program recorded therein.

The above object can be attained by providing a sound signal encodingmethod and apparatus, in which in encoding sound signals from aplurality of channels, an arbitrary number of sine waves are extractedfrom each of the sound signals from the plurality of channels,first-channel information including sine wave information standing on asine wave extracted from a first one of the plurality of channels andsecond-channel information including sine wave information standing on asine wave extracted from a second one of the plurality of channels orsine wave information standing on a predetermined sine wave are used toset one of the sine wave information in the second-channel informationor the sine wave information standing on the predetermined sine wave asa to-be-correlated object for encoding in correlation with each sinewave information in the first-channel information, and the sine waveinformation in the second-channel information is encoded and the sinewave information in the first-channel information is encoded using thecorrelation with the sine wave information set as the to-be-correlatedobject.

Also the above object can be attained by providing a sound signalencoding method and apparatus in which in encoding sine wave informationfrom a first channel, one of sine wave information from a second channelor predetermined sine wave information is set as a to-be-correlatedobject in correlation with the first-channel sine wave information, andthe first-channel sine wave information is encoded using the correlationwith the sine wave information as the to-be-correlated object.

Also the above object can be attained by providing a sound signaldecoding method and apparatus in which in restoring sound signals from aplurality of channels by decoding a sine wave information code obtainedby extracting an arbitrary number of sine waves from each of the soundsignals from the plurality of channels, using first-channel informationincluding sine wave information standing on a sine wave extracted from afirst one of the plurality of channels and second-channel informationincluding sine wave information standing on a sine wave extracted from asecond one of the plurality of channels or sine wave informationstanding on a predetermined sine wave to set one of the sine waveinformation in the second-channel information or the sine waveinformation standing on the predetermined sine wave as ato-be-correlated object for encoding in correlation with each sine waveinformation in the first-channel information, encoding the sine waveinformation in the second-channel information and encoding the sine waveinformation in the first-channel information using the correlation withthe sine wave information set as the to-be-correlated object, the sinewave information in the encoded second-channel information is decoded,the sine wave information in the encoded first-channel information isdecoded using the correlation with the sine wave information set as theto-be-correlated object, and the sound signals from the plurality ofchannels are restored on the basis of the sine wave information in thefirst-channel information and sine wave information in thesecond-channel information.

In the above sound signal decoding method and apparatus, in decoding theencoded first-channel sine wave information using the correlation withone of the second-channel sine wave information or predetermined sinewave information, the encoded second-channel sine wave information isdecoded and then the encoded first-channel sine wave information isdecoded using the correlation with the sine wave information set as theto-be-correlated object.

Also the above object can be attained by providing a sound signalencoding method and apparatus in which in encoding sound signals from aplurality of channels, an arbitrary number of gain control informationare generated correspondingly to the amplitude of the sound signals fromthe plurality of channels for gain control of the sound signals, thegain control information generated for the first-channel sound signaland gain control information generated for the second-channel soundsignal are used to set one of the second-channel gain controlinformation or predetermined gain control information as anto-be-correlated object for encoding in correlation with eachfirst-channel gain control information, the second-channel gain controlinformation is encoded, and the first-channel gain control informationis encoded using the correlation with the gain control information setas the to-be-correlated object.

In the above sound signal encoding method and apparatus, in encoding thefirst-channel gain control information, one of the second-channel gaincontrol information or predetermined gain control information is set asthe to-be-correlated object in correlation with the first-channel gaincontrol information, and the first-channel gain control information isencoded using the correlation with the gain control information as theto-be-correlated object.

Also the above object can be attained by providing a sound signaldecoding method and apparatus in which in restoring sound signals from aplurality of channels by decoding a gain control information codeobtained by generating an arbitrary number of gain control informationcorrespondingly to the amplitude of the sound signals from the pluralityof channels for gain control of the sound signals, using the gaincontrol information generated for the first-channel sound signal andgain control information generated for the second-channel sound signalto set one of the second-channel gain control information orpredetermined gain control information as an to-be-correlated object forencoding in correlation with each first-channel gain controlinformation, encoding the second-channel gain control information, andencoding the first-channel gain control information using thecorrelation with the gain control information set as theto-be-correlated object, the encoded second-channel gain controlinformation is decoded, the encoded first-channel gain controlinformation is decoded using the correlation with the gain controlinformation set as the to-be-correlated object, and gain controlcorrection is made on the basis of the first-channel information andsecond-channel gain control information.

In the above sound signal decoding method and apparatus, in decoding theencoded first-channel gain control information using the correlationwith one of the second-channel gain control information or predeterminedgain control information, the encoded second-channel gain controlinformation is decoded and then the encoded first-channel gain controlinformation is decoded using the correlation with the gain controlinformation set as the to-be-correlated object.

Also the above object can be attained by providing a program allowing acomputer to execute the above sound signal encoding or decoding. Alsothe above object can be attained by providing a computer-readablerecording medium having the program recorded therein.

Also the above object can be attained by providing a recording mediumhaving a sine wave information code or gain control information codeobtained through the sound signal encoding.

These objects and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the best mode for carrying out the present invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the conventional sine wave informationencoder.

FIG. 2 shows an example of sine wave information on right and leftchannels.

FIG. 3 shows, by way of example, differences in amplitude informationbetween the right and left channels Rch and Lch, the informationcorresponding in index to each other, and corresponding numbers ofencoded bits.

FIG. 4 shows, by way of example, differences in phase informationbetween the right and left channels Rch and Lch, the informationcorresponding in index to each other, and corresponding numbers ofencoded bits.

FIG. 5 shows an example of the variable-length code table used forencoding amplitude or phase information.

FIG. 6 shows another example of the sine wave information on the rightand left channels.

FIG. 7 shows, by way of another example, differences in amplitudeinformation between the right and left channels Rch and Lch, theinformation corresponding in index to each other, and correspondingnumbers of encoded bits.

FIG. 8 shows, by way of another example, differences in phaseinformation between the right and left channels Rch and Lch, theinformation corresponding in index to each other, and correspondingnumbers of encoded bits.

FIG. 9 schematically illustrates the sound signal encoder according tothe present invention.

FIG. 10 schematically illustrates the sound signal decoder according tothe present invention.

FIG. 11 schematically illustrates a portion of the sine wave informationencoder included in the sound signal encoder according to the presentinvention, that encodes amplitude information on the right channel Rch.

FIG. 12 shows a flow of operations made in setting a to-be-correlatedobject in the correlation setter in the sine wave information encoder.

FIG. 13 shows, by way of example, differences amplitude information onthe right channel (Rch) and amplitude information on the left channel(Lch), to be correlated with the former, and corresponding numbers ofencoded bits.

FIG. 14 shows, by way of example, differences between phase informationon the right channel (Rch) and phase information on the left channel(Lch), to be correlated with the former, and corresponding numbers ofencoded bits.

FIG. 15 shows, by way of another example, differences between amplitudeinformation on the right channel (Rch) and amplitude information on theleft channel (Lch), to be correlated with the former, and correspondingnumbers of encoded bits.

FIG. 16 shows, by way of another example, differences between phaseinformation on the right channel (Rch) and phase information on the leftchannel (Lch), to be correlated with the former, and correspondingnumbers of encoded bits.

FIG. 17 schematically illustrates a portion of the sine wave informationdecoder included in the sound signal decoder according to the presentinvention, that decodes amplitude information on the right channel Rch.

FIG. 18 illustrates, as one example, the entire sine wave informationencoder.

FIG. 19 shows an example of sine wave information on right and leftchannels.

FIG. 20 shows an example of non-coincidence, in the conventional method,of amplitude or phase information on the right channel Rch withamplitude or phase information on the left channel Lch.

FIG. 21 shows an example of coincidence, in the method according to thepresent invention, of amplitude or phase information on the rightchannel Rch with amplitude or phase information on the left channel Lch.

FIG. 22 illustrates, as one example, the entire sine wave informationdecoder.

FIG. 23 schematically illustrates a portion of the gain controlinformation encoder included in the sound signal encoder according tothe present invention, that encodes gain control information on theright channel Rch.

FIG. 24 shows an example of gain control information on right and leftchannels.

FIG. 25 shows, by way of example, differences between gain controlinformation on the right channel (Rch) and gain control information onthe left channel (Lch), to be correlated with the former, andcorresponding numbers of encoded bits, in the conventional method.

FIG. 26 shows an example of the variable-length code table used forencoding gain control information.

FIG. 27 shows, by way of example, differences between gain controlinformation on the right channel (Rch) and gain control information onthe left channel (Lch), to be correlated with the former, andcorresponding numbers of encoded bits, in the method according to thepresent invention.

FIG. 28 schematically illustrates a portion of the gain controlinformation decoder included in the sound signal decoder according tothe present invention, that decodes gain control information on theright channel Rch.

FIG. 29 shows an example of gain control information on right and leftchannels.

FIG. 30 shows an example of non-coincidence, in the conventional method,of gain control information on the right channel Rch with gain controlinformation on the left channel Lch.

FIG. 31 shows an example of coincidence, in the method according to thepresent invention, of gain control information on the right channel Rchwith gain control information on the left channel Lch.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention is embodied in the modes which will be describedbelow with the accompanying drawings. The embodiments which will bedescribed below are applications of the present invention to a soundsignal encoding apparatus and method, capable of making variable-lengthcoding sine wave information extracted from audio signals from aplurality of channels efficiently with the use of an inter-channelcorrelation, a recording medium having recorded therein a string ofcodes generated by the above variable-length encoding, and a soundsignal decoding apparatus and method, capable of decoding the codestring.

The following description will cover first the general construction ofthe sound signal encoder and decoder according to the present invention,and then the applications of the above sound signal encoder and decoder.It should be noted that in the following description, it is assumed thatthe number of channels are two (2), namely, the audio signals are stereosignals, but it is of course that the present invention is not limitedto this number of channels.

Referring now to FIG. 9, there is schematically illustrated in the formof a block diagram the sound signal encoder according to the presentinvention. The sound signal encoder is generally indicated with areference number 10. As shown in FIG. 9, the sound signal encoder 10includes a frequency band divider 11. The frequency band divider 11 issupplied with an audio signal to be encoded. Using a filter such as QMF(quadrature mirror filter) or PQF (polyphase quadrature filter), thefrequency band divider 11 divides the audio signal into signals of nfrequency subbands. It should be noted that the width of each of thesubbands (will be referred to as “encoded unit” hereafter whereverappropriate) into which an audio signal is divided in frequency by thefrequency band divider 11 may be either uniform or non-uniformcorrespondingly to a critical bandwidth. The frequency band divider 11divides the audio signal into the n encoded units (will be referred toas “first to n-th encoded units” hereafter wherever appropriate), andsupplies them to a sine wave extraction units 12 ₁ to 12 _(n) at everypredetermined time block (frame).

The sine wave extraction units 12.sub.1 to 12.sub.n extract sine wavessuch as tone components from time-based signals in the first to n-thencoded units supplied from the frequency band divider 11. Note that forextraction of the sine wave such as tone component from the time-basedsignal, there may be used the Wiener-proposed Generalized HarmonicAnalysis (GHA) disclosed in the specifications and drawings of theJapanese Patent Application Nos. 2000-380639 and 2001-182384 theInventors already filed, for example. The “Generalized Harmonic Analysis(GHA) is such that a sine wave whose residual energy in an analyzedblock is smallest is extracted from an original time-series signal andsuch an extraction is repeated with respect to the residual signal. Eachof the sine wave extraction units 12.sub.1 to 12.sub.n supply waveformparameter of the extracted sine wave, such as frequency, amplitudeinformation and phase information, to a sine wave information encoder13.

The sine wave information encoder 13 encodes sine wave information suchas frequency, amplitude information and phase information supplied fromthe sine wave extraction units 12 ₁ to 12 _(n). At this time, the sinewave information encoder 13 makes variable-length coding of theamplitude information and phase information using a correlation betweenthe right and left channels efficiently. The sine wave informationencoder 13 supplies the sine wave information code thus obtained to amultiplexer 21.

The sound signal encoder 10 also includes gain controllers 14 ₁ to 14_(n). These gain controllers 14 ₁ to 14 _(n) generate gain controlinformation according to the amplitudes of the residual signals in theanalyzed blocks and control the gains of signals in the analysis blocksaccording to the gain control information. The gain controllers 14 ₁ to14 _(n) supply the gain control information to a gain controlinformation encoder 15, and signals in the first to n-th encoded unitsresulted from the gain control to spectrum transform units 16 ₁ to 16_(n).

The gain control information encoder 15 encodes the gain controlinformation supplied from the gain controllers 14 ₁ to 14 _(n). The gaincontrol information encoder 15 supplies the gain control informationcode thus obtained to the multiplexer 21.

The spectrum transform units 16 ₁ to 16 _(n) make spectrum transformsuch as MDCT (modified discrete cosine transform) of the time-basedsignals supplied from the gain controllers 14 ₁ to 14 _(n) to generatefrequency-based spectrum signals to quantization accuracy selection unit17 and normalization units 18 ₁ to 18 _(n).

The quantization accuracy selection unit 17 selects a quantization stepfor quantizing to-be-normalized data of the first to n-th encoded unitson the basis of the spectrum signals of the first to n-th encoded unitssupplied from the spectrum transform units 16 ₁ to 16 _(n). Then, thequantization accuracy selection unit 17 supplies the quantizationaccuracy information on the first to n-th encoded units corresponding tothe selected quantization step to a quantization accuracyinformation/normalization coefficient encoder 19 and quantizers 20 ₁ to20 _(n).

The normalization units 18 ₁ to 18 _(n) extract a one, whose absolutevalue is largest, of components of spectrum signals in the first to n-thencoded units, and take a coefficient corresponding to the maximum valueas a normalization coefficient for the first to n-th encoded units. Thenormalization units 18 ₁ to 18 _(n) normalize (divide) the components ofthe spectrum signals in the first to n-th encoded units with (by) valuescorresponding to the normalization coefficients for the first to n-thencoded units. In this case, the to-be-normalized data obtained throughthe normalization ranges from −1.0 to 1.0. The normalization units 18 ₁to 18 _(n) supply the normalization coefficients for the first to n-thencoded units to the quantization accuracy information/normalizationcoefficient encoder 19 and the to-be-normalized data on the first ton-th encoded units to the quantizers 20 ₁ to 20 _(n).

The quantization accuracy information/normalization coefficient encoder19 encodes the quantization accuracy information supplied from thequantization accuracy selector 17 and normalization coefficients fromthe normalization units 18 ₁ to 18 _(n). For encoding the quantizationaccuracy information and normalization coefficients, there may be usedthe technique disclosed in the specification and drawings in theJapanese Patent Application No. 2000-390589 the Inventors filed already,for example. That is, the encoding can be done with an improvedefficiency through the variable-length encoding using a correlationbetween adjacent encoded units, adjacent channels or adjacent times. Thequantization accuracy information/normalization coefficient encoder 19supplies the quantization accuracy information code and normalizationinformation code thus obtained to the multiplexer 21.

The quantizers 20 ₁ to 20 _(n) encode the to-be-normalized data in thefirst to n-th encoded units at the quantization steps corresponding othe quantization accuracy information in the first to n-th encodedsteps, and supply quantization coefficients thus obtained for the firstto n-th encoded units to the multiplexer 21.

The multiplexer 21 multiplexes the quantization coefficients for thefirst to n-th encoded units with the gain control information code,quantization accuracy information code and normalization informationcode. The multiplexer 21 transmits or records a code string resultedfrom the multiplexing to a recording medium (not shown).

As above, the sound signal encoder 10 according to the present inventionextracts sine waves such as tone components from the input audio signaland encode the waveform parameters such as frequency, amplitudeinformation and phase information. At this time, variable-length codingis made of the amplitude information and phase information by theefficient use of the correlation between the right and left channels.Also, the encoder 10 encodes the residual signal resulted fromextraction of sine waves from the audio signal after completion of thespectrum transform such as MDCT, for example.

Referring now to FIG. 10, there is schematically illustrated in the formof a block diagram the sound signal decoder according to the presentinvention, generally indicated with a reference number 30. The soundsignal decoder 30 is supplied with a code string transmitted from thesound signal encoder 10 or supplied from the sound signal encoder 10 viaa recording medium.

As shown in FIG. 10, the sound signal decoder 30 includes ademultiplexer 31 which decodes the input code string into thequantization coefficients, quantization accuracy information code,normalization information code, gate control information code and sinewave information code in the first to n-th encoded units. Thedemultiplexer 31 supplies the quantization coefficients in the first ton-th encoded units to the dequantizers 33 ₁ to 33 _(n) corresponding tothe encoded units, respectively, and the quantization accuracyinformation code and normalization information code in the first to n-thencoded units to a quantization accuracy information/normalizationcoefficient decoder 32. Also, the demultiplexer 31 supplies the gaincontrol information code and sine wave information code to a gaincontrol information decoder 36 and sine wave information decoder 38,respectively.

The quantization accuracy information/normalization coefficient decoder32 decodes the supplied quantization accuracy information code andnormalization information code and supplies the decoded quantizationaccuracy information and normalization coefficient to the dequantizer 33₁ to 33 _(n) and denormalization units 34 ₁ to 34 _(n), respectively.

The dequantizers 33 ₁ to 33 _(n) dequantize the quantizationcoefficients in the first to n-th encoded units at quantization stepscorresponding to the quantization accuracy information in the encodedunits to generate to-be-normalized data on the first to n-th encodedunits. The dequantizers 33 ₁ to 33 _(n) supply the to-be-normalized dataon the first to n-th encoded units to the denormalization units 34 ₁ to34 _(n).

The denormalization units 34 ₁ to 34 _(n) decode the to-be-normalizeddata on the first to n-th encoded units supplied from the dequantizers33 ₁ to 33 _(n) by multiplying the data by values corresponding to thenormalization information in the first to n-th encoded units,respectively, to generate spectrum signals for the first to n-th encodedunits. The denormalization units 34 ₁ to 34 _(n) supply the spectrumsignals for the first to n-th encoded units to inverse spectrumtransform units 35 ₁ to 35 _(n).

The inverse spectrum transform units 35 ₁ to 35 _(n) make inversespectrum transform such as IMDCT (inverse MDCT) of the spectrum signalsfor the first to n-th encoded units supplied from the denormalizationunits 34 ₁ to 34 _(n) to generate a time-based signal and supply thetime-based signal to gain controllers 37 ₁ to 37 _(n).

The gain control information decoder 36 which decodes the gain controlinformation codes for the first to n-th encoded units and supplies thedecoded gain control information to the gain controllers 37 ₁ to 37 _(n)corresponding to the respective encoded units.

The gain controllers 37 ₁ to 37 _(n) make gain control correction of thesignals in the first to n-th encoded units on the basis of the gaincontrol information supplied from the gain control information decoder36, and supply the residual signals for the first to n-th encoded unitsto sine wave synthesizers 39 ₁ to 39 _(n).

The sine wave information decoder 38 decodes the sine wave informationcode, and supplies the decoded sine wave information, that is, frequencyinformation, amplitude information and phase information to the sinewave synthesizers 39 ₁ to 39 ₄. At this time, the sine wave informationdecoder 38 makes variable-length decoding of the amplitude informationand phase information with the efficient utilization of the correlationbetween the right and left channels.

The sine wave synthesizers 39 ₁ to 39 ₄ generate sine waves of the firstto n-th encoded units on the basis of the sine wave information suppliedfrom the sine wave information decoder 38, and combine the sine waveswith the residual signals of the first to n-th encoded units suppliedfrom the gain controllers 37 ₁ to 37 _(n) to generate signals of thefirst to n-th encoded units. The sine wave synthesizers 39 ₁ to 39 ₄supply the signals of the first to n-th encoded units to a frequencyband synthesizer 40.

The frequency band synthesizer 40 combines together the frequency bandsof the signals of the first to n-th encoded units supplied from the sinewave synthesizers 39 ₁ to 39 ₄ to restore the original audio signal.

As above, the sound signal decoder 30 according to the present inventiongenerates a sine wave on the basis of sine wave information such asfrequency information, amplitude information and phase informationincluded in an input code string. At this time, it makes variable-lengthdecoding of the amplitude information and phase information withefficient utilization of a correlation between the right and leftchannels. The sound signal decoder 30 decodes quantization coefficientincluded in the input code string, and make inverse spectrum transformsuch as IMDCT, for example, of the quantization coefficient to generatea time-based signal. Then the sound signal decoder 30 combines the sinewave thus obtained with a residual signal to restore an original audiosignal.

The aforementioned sine wave information encoder 13 can makehigher-efficiency variable-length coding of waveform parameters such asamplitude information and phase information by utilizing the correlationbetween the right and left channels efficiently. So, the constructionand operation of the sine wave information encoder 13 will be describedin detail below. It should be noted that although the description of theconstruction and operation will be made concerning amplitudeinformation, it is also quite true of phase information. Also, it isassumed in the following description that a number N_(L) of sine waveshave been extracted on the left channel Lch while a number N_(R) of sinewaves have been extracted on the right channel Rch.

A portion of the sine wave information encoder 13, that encodesamplitude information on the right channel Rch, is schematicallyillustrated in FIG. 11. As shown in FIG. 11, the sine wave informationencoder 13 includes a left-channel frequency information holder 50,right-channel frequency information holder 51, to-be-correlated objectsetter 52, left-channel amplitude information holder 53, right-channelamplitude information holder 54, storage unit 55, to-be-correlatedobject selector 56, adder-subtracter 57, and a variable-length encoder58.

The left-channel frequency information holder 50 indexes a number N_(L)of sine waves extracted from the left channel Lch by 0 to N_(L)−1,respectively, sequentially starting with the lowest-frequency one, andholds the sine waves in correspondence to the indexes. Similarly, theright-channel amplitude information holder 51 indexes a number N_(R) ofsine waves extracted from the right channel Rch by 0 to N_(R)−1,respectively, sequentially starting with the lowest-frequency one, andholds the sine waves in correspondence to the indexes.

The to-be-correlated object setter 52 sets one of sine waves on theleft-channel Lch, that is to be paired, namely, correlated, with a sinewave on the right channel Rch, from which the left-channel sine wave isto be subtracted, on the basis of the number N_(L) of left-channelfrequency information held in the left-channel frequency informationholder 50 and the number N_(R) of right-channel frequency informationheld in the right-channel frequency information holder 51. Namely, thesetter 52 sets a sine wave on the left channel Lch, that is to besubtracted from with a sine wave on the right-channel Rch, to provide adifference (Rch−Lch).

The above setting of a to-be-correlated object will be described indetail below with reference to the flow chart in FIG. 12. First, in stepS1, the setter 52 sets min_distance to FREQ_MAX. The “FREQ_MAX” is avalue exceeding a maximum value the frequency information can take,namely, a value exceeding an absolute value of a difference between twofrequencies. For example, in case the frequency information freq is0≦freq<128, FREQ_MAX should be set to 128.

Next in step S2, the setter 52 sets an index i of 0. The “index i”indicates an index of the sine wave on the right channel Rch, and it is0≦i<N_(R).

Then in step S3, the setter 52 judges whether the index i is smallerthan N_(R). If the index i is smaller than N_(R) (YES), the setter 52goes to step S4. If the index i is not smaller than N_(R) (NO), namely,when it is larger than N_(R), the setter 52 exits the to-be-correlatedobject setting.

In step S4, the setter 52 sets an index j of 0. The “index j” is anindex of the sine wave on the left channel Lch, and it is 0≦j<N_(L).

In step S5, the setter 52 judges whether the index j is smaller thanN_(L). If the index j is smaller than N_(L) (YES), the setter 52 goes tostep S6. If the index j is not N_(L) (NO), namely, if it is larger thanN_(L), the setter 52 goes to step S10.

Next in step S6, the setter 52 calculates an absolute difference betweenthe i-th frequency information read from the right-channel frequencyinformation holder 51 (see FIG. 11) and j-th frequency information readfrom the left-channel frequency information holder 50 (also see FIG.11), and takes it as “distance”.

In step S7, the setter 52 judges whether the “distance” is smaller thanthe min_distance. If the “distance” is smaller than the min_distance(YES), the setter 52 goes to step S8 where it will re-set themin_distance and stores the index j at this time as a min_index. On thecontrary, if the “distance” is larger than the min_distance (NO), thesetter 52 goes to step S9.

In step S9, the setter 52 increments the index j by one, and returns tostep S5 where it will repeat operations similar to the above N_(L) timesuntil the index j becomes N_(L)−1. As a result, the min_index is of thefrequency information on the left channel Lch, whose absolute differencefrom the i-th frequency information on the right channel Rch issmallest.

In step S10, the setter 52 judges whether the min_index is smaller thana predetermined threshold, that is, two (20, for example. If the index jis smaller than 2 (YES), namely, if it is 0 or 1, the setter 52 goes tostep S11. On the contrary, if the index j is not smaller than 2 (NO),namely, if the min_index is larger than 2, the setter 52 goes to stepS12. It should be noted that although the threshold is “2” in thisexample, this is just an example and an optimum value may be selectedfrom a range of value the frequency information can taken.

In step S11, the setter 52 sets an index [i] of the min_index. The“index [i]” indicates an index of amplitude information on the leftchannel Lch, which is to be paired with the i-th amplitude informationon the right channel Rch, namely, an object which is to be subtractedfrom the amplitude information on the right channel Rch is calculated inthe encoding technique using an inter-channel difference.

In step S12, the setter 52 judges whether the index i is smaller thanN_(L). If it is determined in step S12 that the index i is smaller thanN_(L) (YES), it means that the left channel Lch has no sine waveinformation having any frequency near that of the i-th sine waveinformation on the right channel Rch. In this case, the setter 52 goesto step S13 where the setter 52 will set the index [i] to i, namely, anobject which is to be subtracted from the i-th sine wave information onthe right channel Rch, to the i-th sine wave information on the leftchannel Lch. On the contrary, if it is determined in step S12 that theindex i is larger than N_(L) (NO), it means that the left channel Lchhas no object which is to be subtracted from the i-th sine wave on theright channel Rch. In this case, the setter 52 goes to step S14 where itwill set the index [i] to a provisional value, for example, −1. Itshould be noted that in this case, a preset default value will besubtracted from the i-th sine wave on the right channel Rch.

In step S15, the setter 52 increments the index i by one, and thenreturns to step S3 where it will repeat operations similar to the aboveN_(R) times until the index i becomes N_(R)−1.

All the indexes [i] are set to any of min_index, i and −1 as above. Thatis, the to-be-correlated object setter 52 sets a sine wave on the leftchannel Lch, whose frequency-based distance is smaller than thethreshold, as an object to be subtracted from the sine wave on the rightchannel Rch. In case no sine wave smaller than the threshold exists onthe left channel Lch, the setter 52 will set a sine wave having the sameindex on the left channel Lch as the object. If there are not on theleft channel Lch any sine waves having the same index, for example, ifthe number of sine waves extracted from the right channel Rch is largerthan the number of sine waves extracted from the left channel Lch, thesetter 52 will set a default value as the object.

Now, the to-be-correlated object setter 52 supplies the index [i] havingbeen set as above to the to-be-correlated object selector 56 as will bedescribed with reference to FIG. 11 again.

As shown in FIG. 11, the left-channel amplitude information holder 53indexes a number N_(L) of sine waves extracted from the left channel Lchby 0 to N_(L)−1, respectively, sequentially starting with thelowest-frequency one, and holds amplitude information and phaseinformation in correspondence to the indexes. Similarly, theright-channel amplitude information holder 54 indexes a number N_(R) ofsine waves extracted from the right channel Rch by 0 to N_(R)−1,respectively, sequentially starting with the lowest-frequency one, andholds amplitude information and phase information in correspondence tothe indexes. The storage unit 55 holds the preset default values. Thedefault values should preferably be set to an intermediate value ofpossible amplitude information, a mean value determined based on thefrequency of appearance or the highest frequency of appearance. Bysetting the default value to such a value, it is expectable that thedifference calculated as will be described later will take a smallervalue.

The to-be-correlated object selector 56 selects an object which is to besubtracted from the i-th right-channel amplitude information accordingto the index [i] supplied from the to-be-correlated object setter 52.More particularly, when the index [i] is −1, the to-be-correlated objectselector 56 reads the preset default value from the storage unit 55.When the index [i] is other than −1, the selector 56 will read the index[i]-th amplitude information from the left-channel amplitude informationholder 53. The to-be-correlated object selector 56 supplies theamplitude information or default value thus read to the adder-subtracter57.

The adder-subtracter 57 calculates a difference by subtracting the index[i]-th amplitude information on the left-channel Lch supplied from theright-channel amplitude information holder 54 or default value from thei-th amplitude information read from the left-channel to-be-correlatedobject selector 56, and supplies the difference thus calculated to thevariable-length encoder 58.

The variable-length encoder 58 makes variable-length coding of thedifference supplied from the adder-subtracter 57 according to thevariable-length code table to generate a variable-length code of thedifference of the amplitude information on the right channel Rch.

The aforementioned technique of coding will be used here to check theefficiency of coding when the sine wave information as shown in FIGS. 2and 6 is supplied. It should be noted that in this example, theamplitude information and phase information are to be encoded with 3bits, respectively, when they have not been compressed.

First, it is assumed that the sine wave information is given as shown inFIG. 2. For encoding amplitude information with the use of the encodingtechnique according to the present invention, amplitude information onthe left channel Lch, indexed by n (=0, 1, 2, 3), respectively, are setas objects which are to be subtracted from amplitude information on theright channel Rch, also indexed by n (=0, 1, 2, 3), respectively. Thus,the difference resulted from subtraction of the amplitude information onthe left channel Lch from the amplitude information on the right channelRch will be as shown in FIG. 13. By encoding the difference using thevariable-length code table shown in FIG. 4, it is possible to encode theamplitude information on the right channel Rch with a total of 5 bits.This number of bits is 7 bits smaller than 12 bits (=3 bits×4) when thephase information is not compressed.

Similarly, for encoding phase information, phase information on the leftchannel Lch, indexed by n (=0, 1, 2, 3), respectively, are set asobjects which are to be subtracted from phase information on the rightchannel Rch, also indexed by n (=0, 1, 2, 3), respectively. Thus, thedifference resulted from subtraction of the phase information on theleft channel Lch from the phase information on the right channel Rchwill be as shown in FIG. 14. By encoding the difference using thevariable-length code table shown in FIG. 4, it is possible to encode thephase information on the right channel Rch with a total of 5 bits. Thisnumber of bits 7 bits smaller than 12 bits (=3 bits×4) when the phaseinformation is not compressed.

Next, it is assumed that the sine wave information is given as shown inFIG. 6. For encoding amplitude information with the use of the encodingtechnique according to the present invention, amplitude information onthe left channel Lch, indexed by n=0 and 1, respectively, are set asobjects which are to be subtracted from amplitude information on theright channel Rch, indexed by n=1 and 2, respectively. A default valueis se to 4 for example as an object to be subtracted from the amplitudeinformation on the right channel Rch, indexed by n=2, while amplitudeinformation on the left channel Lch, index by n=3, is as an object to besubtracted from the amplitude information on the right channel Rch, alsoindexed by n=3. Thus, the difference resulted from subtraction of theamplitude information on the left channel Lch or default value from theamplitude information on the right channel Rch, corresponding to theleft0channel amplitude information or the default value, will be asshown in FIG. 15. By encoding the difference using the variable-lengthcode table shown in FIG. 4, it is possible to encode the amplitudeinformation on the light channel Rch with a total of 5 bits. This numberof bits is 9 bits smaller than 14 bits which can be attained with theconventional technique as shown in FIG. 7, and 7 bits smaller than 12bits when the phase information is not compressed.

Similarly, for encoding phase information, phase information on the leftchannel Lch, indexed by n=0 and 1, respectively, are set as objectswhich are to be subtracted from phase information on the right channelRch, indexed by n=1 and 2, respectively. A default value is se to 4 forexample as an object to be subtracted from the phase information on theright channel Rch, indexed by n=2, while phase information on the leftchannel Lch, having an index n=3, is as an object to be subtracted fromthe phase information on the right channel Rch, also indexed by n=3.Thus, the difference resulted from subtraction of the phase informationon the left channel Lch or default value from the phase information onthe right channel Rch, corresponding to the left0channel phaseinformation or the default value, will be as shown in FIG. 16. Byencoding the difference using the variable-length code table shown inFIG. 4, it is possible to encode the phase information on the rightchannel Rch with a total of 7 bits. This number of bits is 17 bitssmaller than 24 bits which can be attained with the conventionaltechnique as shown in FIG. 8, and 5 bits smaller than 12 bits when thephase information is not compressed.

Next, the construction and operation of the sine wave informationdecoder 38 which decodes a sine wave information code will be describedin detail below. It should be noted that although the description of theconstruction and operation will be made concerning amplitude informationsimilarly to the sine wave information encoder 13, it is also quite trueof phase information.

A portion of the sine wave information decoder 38, that decodesamplitude information on the right channel Rch, is schematicallyillustrated in FIG. 17. As shown in FIG. 17, the sine wave informationdecoder 38 includes a left-channel frequency information holder 60,right-channel frequency information holder 61, to-be-correlated objectsetter 62, left-channel amplitude information holder 63, storage unit64, to-be-correlated object selector 65, variable-length decoder 66,adder 67 and a right-channel amplitude information holder 68.

The left-channel frequency information holder 60 indexes a number N_(L)of sine waves extracted from the left channel Lch by 0 to N_(L)−1,respectively, sequentially starting with the lowest-frequency one, andholds the sine waves in correspondence to the indexes. Similarly, theright-channel amplitude information holder 61 indexes a number N_(R) ofsine waves extracted from the right channel Rch 0 to N_(R)−1,respectively, to by sequentially starting with the lowest-frequency one,and holds the sine waves in correspondence to the indexes.

Similarly to the aforementioned to-be-correlated object setter 52 in thesine wave information encoder 13, the to-be-correlated object setter 62sets one of sine waves on the left-channel Lch, that is to be paired,namely, correlated, with a sine wave on the right channel Rch, fromwhich the left-channel sine wave is to be subtracted, on the basis ofthe number N_(L) of left-channel frequency information held in theleft-channel frequency information holder 60 and the number N_(R) ofright-channel frequency information held in the right-channel frequencyinformation holder 61. An index [i] thus provided indicates either theorder of the amplitude information on the left channel Lch, which hasbeen subtracted from the i-th amplitude information on the right channelRch, or a default value. The to-be-correlated object setter 62 suppliesthe index [i] thus set to the to-be-correlated object selector 65.

The left-channel amplitude information holder 63 indexes the numberN_(L) of sine waves extracted from the left channel Lch by 0 to N_(L)−1,respectively, sequentially starting with the lowest-frequency one, andholds the sine waves in correspondence to the indexes. The storage unit64 will hold a pre-set default value. The default value takes the samevalue as that held in the aforementioned storage unit 55 included in thesine wave information encoder 13.

Similarly to the aforementioned to-be-correlated object selector 56 inthe sine wave information encoder 13, the to-be-correlated objectselector 65 selects an object having been subtracted from theright-channel i-th amplitude information according to the index [i]supplied from the to-be-correlated object setter 62. More particularly,when the index [i] is −1, the to-be-correlated object selector 65 readsthe preset default value from the storage unit 64. In any other case,the to-be-correlated object selector 65 will read the index [i]-thamplitude information from the left-channel amplitude information holder63. The to-be-correlated object selector 65 supplies the amplitudeinformation or default value thus read to the adder 67.

The variable-length decoder 66 make variable-length coding of avariable-length code of the difference of the amplitude information onthe right channel Rch, included in the code string, and supplies thedifference of the amplitude information on the right channel Rch, thusobtained, to the adder 67.

The adder 67 adds the index [i]-th amplitude information on the leftchannel Lch or default value supplied from the to-be-correlated objectselector 65 to the difference on the i-th amplitude information on theright channel Rch, supplied from the variable-length decoder 66 todecode the i-th amplitude information on the right channel Rch. Theadder 67 restores all the N_(R) pieces of amplitude information 0 toN_(R)−1 on the right channel Rch in the similar manner, and suppliesthem to the right-channel amplitude information holder 68.

Since the sine wave information decoder 38 can set a to-be-correlatedobject on the basis of frequency information, if preset, so it is notnecessary to append any information indicative of a to-be-correlatedobject to the code string. In the above technique of decoding, however,amplitude information and phase information on the left channel Lch haveto be decoded before decoding the amplitude information and phaseinformation on the right channel Rch.

The sine wave information encoder 13 may be composed mainly of afrequency information encoder 70, amplitude information encoder 80 and aphase information encoder 90 as shown in FIG. 18.

The frequency information encoder 70 includes encoders 71 ₁ to 71 ₄. Theencoders 71 ₁ to 71 ₄ encode frequency information with differenttechniques of coding, respectively, and supply frequency informationcodes thus generated to a terminal thereof connected to a switch 73.Each of the encoders 71 ₁ to 71 ₄ calculates a required number ofencoding bits as a result of the frequency information coding, andsupplies the result of calculation to an optimum encoding techniqueselector 72. The optimum encoding technique selector 72 selects one ofthe encoders 71 ₁ to 71 ₄ that has supplied a smallest one of therequired numbers of encoding bits supplied from the encoders 71 ₁ to 71₄, and controls the switch 73 so that the frequency information encodedby the encoder 71 will be supplied to the multiplexer 21 (as in FIG. 9).The optimum encoding technique decider 72 supplies an index for theencoding technique taken by the selected encoder 71 to the multiplexer21.

The amplitude information encoder 80 includes encoders 81 ₁ to 81 ₄. Theencoders 81 ₁ to 81 ₄ encode amplitude information with differenttechniques of coding, respectively, and supply amplitude informationcodes thus generated to a terminal thereof connected to a switch 83, anda required number of encoding bits as the result of encoding to anoptimum encoding technique selector 82. The optimum encoding techniqueselector 82 selects one of the encoders 81 ₁ to 81 ₄ that has supplied asmallest one of the required numbers of encoding bits supplied from theencoders 81 ₁ to 81 ₄, and controls the switch 83 so that the amplitudeinformation encoded by the encoder 81 will be supplied to themultiplexer 21 (as in FIG. 9). The optimum encoding technique decider 82supplies an index for the encoding technique taken by the selectedencoder 81 to the multiplexer 21.

The phase information encoder 90 includes encoders 91 ₁ to 91 ₄. Theencoders 91 ₁ to 91 ₄ encode phase information with different techniquesof coding, respectively, and supply phase information codes thusgenerated to terminals thereof connected to a switch 93, and a requirednumber of encoding bits as the result of encoding to an optimum encodingtechnique selector 92. The optimum encoding technique selector 92selects one of the encoders 91 ₁ to 91 ₄ that has supplied a smallestone of the required numbers of encoding bits supplied from the encoders91 ₁ to 91 ₄, and controls the switch 93 so that the phase informationencoded by the encoder 91 will be supplied to the multiplexer 21 (as inFIG. 9). The optimum encoding technique decider 92 supplies an index forthe encoding technique taken by the selected encoder 91 to themultiplexer 21.

The method of encoding sine wave information according to the presentinvention is applicable one of the plurality of encoding techniques inthe amplitude information encoder 80 and phase information encoder 90.It should be noted that it is assumed that frequency information (notshown) is supplied along with the amplitude information and phaseinformation to the amplitude information encoder 80 and phaseinformation encoder 90. It has been described above that each of thefrequency information encoder 70, amplitude information encoder 80 andphase information encoder 90 has four different techniques of coding.However, it is just an example. The present invention is not limited tothe example.

In case the right and left channels are coincident in amplitude or phaseinformation with each other, the encoding of amplitude or phaseinformation on the right channel Rch, for example, may be omitted andonly an index for the technique of coding be supplied to the multiplexer21.

For example, it is assumed here that the sine wave information is givenas shown in FIG. 19. With the conventional technique of coding, thedifference in information between the right and left channels iseffected using the same index. So, the amplitude information on theright channel Rch and that on the left channel Lch are not coincidentwith each other (FALSE) as shown in FIG. 20, with the result that thetechnique of coding with supply of only an index for the encodingtechnique to the multiplexer 21 as above cannot be selected.

With the encoding technique according to the present invention,amplitude information on the left channel Lch, indexed by 0, 1 and 2,respectively, are set as objects to be subtracted from those on theright channel Rch, indexed by 0, 1 and 2, respectively, as shown in FIG.21. Thus, since all the amplitude on the right channel Rch arecoincident with those on the left channel Lch (TRUE), coding of theamplitude information on the right channel Rch may be omitted only withsupply of the encoding technique indexes to the multiplexer 21.

The encoding of amplitude information and phase information in sine waveinformation on one channel as objects to be subjected from correspondingones on the other has been explained by way of example. Also in caseonly one of the amplitude information and phase information iscoincident with the corresponding one, only the index of the encodingtechnique may be encoded without encoding the coincident information.

Also, the sine wave information decoder 38 may be composed of afrequency information decoder 100, amplitude information decoder 110 anda phase information decoder 120 as shown in FIG. 22.

The frequency information decoder 100 includes a switch 101 which issupplied with a frequency information code and encoding technique indexand provides such a control that the frequency information code will besupplied to a decoder 102 corresponding to the encoder 71 selected bythe frequency information encoder 70. The decoder 102 includes alsodecoders 102 ₁ to 102 ₄. The decoders 102 ₁ to 102 ₄ decode thefrequency information code with different decoding techniques,respectively, corresponding to the encoders 71 ₁ to 71 ₄ in thefrequency information encoder 70. The frequency information decoder 100includes also a switch 103 which is supplied with an encoding techniqueindex and provides such a control that frequency information decoded bythe selected decoder 102 will be supplied.

The amplitude information decoder 110 includes a switch 111 which issupplied with an amplitude information code and encoding technique indexand provides such a control that the amplitude information code will besupplied to a decoder 112 corresponding to the encoder 81 selected bythe amplitude information encoder 80. The decoder 112 includes alsodecoders 112 ₁ to 112 ₄. The decoders 112 ₁ to 112 ₄ decode theamplitude information code with different decoding techniques,respectively, corresponding to the encoders 81 ₁ to 81 ₄ in theamplitude information encoder 80. The amplitude information decoder 110includes also a switch 113 which is supplied with an encoding techniqueindex and provides such a control that amplitude information decoded bythe selected decoder 112 will be supplied.

The phase information decoder 120 includes a switch 121 which issupplied with a phase information code and encoding technique index andprovides such a control that the phase information code will be suppliedto a decoder 122 corresponding to the encoder 91 selected by the phaseinformation encoder 90. The decoder 122 includes also decoders 122 ₁ to122 ₄. The decoders 122 ₁ to 122 ₄ decode the phase information codewith different decoding techniques, respectively, corresponding to theencoders 91 ₁ to 91 ₄ in the phase information encoder 90. The phaseinformation decoder 120 includes also a switch 123 which is suppliedwith an encoding technique index and provides such a control that phaseinformation decoded by the selected decoder 122 will be supplied.

The method of decoding sine wave information according to the presentinvention is applicable one of the plurality of encoding techniques inthe amplitude information encoder 110 and phase information encoder 120.It has been described above that each of the frequency informationdecoder 100, amplitude information decoder 110 and phase informationdecoder 120 has four different techniques of coding. However, it is justan example. The present invention is not limited to the example.

Note that the encoding technique according to the present invention isapplicable not only to the coding of aforementioned sine waveinformation but to coding of other information, for example, the gaincontrol information as the gain control information encoder 15 shown inFIG. 9.

As disclosed in the specification and drawings of the Japanese PatentApplication No. 2001-182093 the Inventors of the present inventionalready filed, the gain controllers 14 ₁ to 14 _(n) detect whether thereexists in a signal in a block an attack part that suddenly rises inlevel or a release part, following the attack part, that suddenly fallsin level. If such an attack part or release part exists, the gaincontrollers 14 ₁ to 14 _(n) generate gain-controlled amount informationindicating a gain-controlled amount corresponding to a signal level of apart existing temporally before the attack part and low in level or thelevel of the release part, gain-controlled position informationindicating a position where the gain is controlled correspondingly tothe gain-controlled amount and information on gain-controlled number ofpails indicating a number of gain-controlled parts as gain controlinformation.

The gain control information encoder 15 encodes the above gain controlinformation. At this time, with the gain-controlled position informationbeing taken as the aforementioned frequency information in the sine waveinformation and gain-controlled amount information being taken as theaforementioned amplitude or phase information, the gain controlinformation can be encoded.

Of the gain control information encoder 15, a part which encodes thegain-controlled amount information on the right channel Rch isschematically illustrated in FIG. 23. The gain control informationencoder 15 is composed of a left-channel gain-controlled positioninformation holder 130, right-channel gain-controlled positioninformation holder 131, to-be-correlated object setter 132, left-channelgain-controlled amount information holder 133, right-channelgain-controlled amount information holder 134, storage unit 135,to-be-correlated object selector 136, adder-subtracter 137 and avariable-length encoder 138 as shown in FIG. 23.

Since the technique of encoding the gain-controlled amount informationon the right channel Rch in the gain control information encoder 15 issimilar to the aforementioned technique of encoding amplitude or phaseinformation, so it will not be described in detail. Briefly, it is suchthat a to-be-correlated object is set on the basis of indexedgain-controlled position information on the right and left channels anda difference resulted from subtraction of gain-controlled amountinformation being the correlated object on the left channel Lch fromgain-controlled amount information on the right channel Rch is subjectedto variable-length coding.

It is assumed here that gain control information is given as shown inFIG. 28. For encoding gain-controlled amount information, theconventional technique of coding calculates a difference betweeninformation having the same indexes. So, the difference resulted fromsubtraction of gain-controlled amount information on the left channelLch, having an index n, from gain-gain controlled amount information onthe right channel Rch, having the same index n, will be as shown in FIG.25. By making variable-length coding of the difference according to thevariable-length code table as shown in FIG. 26, for example, thegain-controlled amount information on the right channel Rch can beencoded with a total of 10 bits.

With the encoding method according to the present invention,gain-controlled amount information on the left channel Lch, indexed by0, 2, 3 and 3, respectively, are set as objects to be subtracted fromgain-controlled amount information on the right channel Rch, indexed by0, 1, 2 and 3, respectively. Thus, the difference resulted fromsubtraction of gain-controlled amount information on the left channelLch, set as a to-be-correlated object, from correspondinggain-controlled amount information on the right channel Rch is as shownin FIG. 27. By encoding the difference according to the variable-lengthcode table shown in FIG. 26, the gain-controlled amount information onthe right channel Rch can be encoded with a total of 6 bits, which is 4bits more efficient than the convention technique of coding.

On the other hand, of the gain control information decoder 36 (see FIG.10) which decodes the gain control information code, a part whichdecodes the gain-controlled amount information on the right channel Rchis schematically illustrated in FIG. 28. The gain control informationdecoder 36 is composed of a left-channel gain-controlled positioninformation holder 140, right-channel gain-controlled positioninformation holder 141, to-be-correlated object setter 142, left-channelgain-controlled amount information holder 143, storage unit 144,to-be-correlated object selector 145, variable-length decoder 146, adder147 and a right-channel gain-controlled amount information holder 148,as shown in FIG. 28.

Since the technique of encoding a gain-controlled amount informationcode on the right channel Rch in the gain control information decoder 36is similar to the aforementioned technique of encoding an amplitude orphase information code, it will not be described in detail. Briefly, ato-be-correlated object is set on the basis of indexed right- andleft-channel gain-controlled position information, and thegain-controlled amount information on the right channel Rch is restoredby adding together a difference of gain-controlled amount information onthe right channel Rch from corresponding gain-controlled amountinformation on the left channel Lch and gain-controlled amountinformation, as an object to be correlated, on the left channel Lch or adefault value are added together to restore.

As in the coding of sine wave information, in case all thegain-controlled amounts on the right channel Rch are the same as thoseon the left channel Lch, the coding of the gain-controlled amountinformation on the right channel Rch, for example, is omitted and onlyan encoding technique index may be supplied to the multiplexer 21.

For example, it is assumed here that sine wave information is given asshown in FIG. 29. With the conventional technique of coding, thedifference in information between the right and left channels iseffected using the same index. So, the gain-controlled amountinformation on the right channel Rch and that on the left channel Lchare not coincident with each other (FALSE) as shown in FIG. 30, with theresult that the technique of coding with supply of only an index for theencoding technique to the multiplexer 21 as above cannot be selected.

With the encoding technique according to the present invention,gain-controlled amount information on the left channel Lch, indexed by1, 2 and 3, respectively, are set as objects to be subtracted from thoseon the right channel Rch, indexed by 0, 1 and 2, respectively, as shownin FIG. 31. Thus, since all the gain-controlled amount information onthe right channel Rch are coincident with those on the left channel Lch(TRUE), coding of the gain-controlled amount information on the rightchannel Rch may be omitted only with supply of the encoding techniqueindexes to the multiplexer 21.

Note that the present invention is not limited to the embodiments havingbeen described in the foregoing but it can of course be modified invarious other forms without departing from the scope and spirit thereof.

The sound signal encoder according to the present invention has beendescribed as a one which encodes an audio signal divided into frequencysubbands, extracting a sine wave such as tone component from theaudio-signal subbands, encoding the sine wave information and makingspectrum transform of a residual signal of the audio signal from whichthe sine wave has been extracted. However; the present invention is notlimited to the sound signal encoder thus constructed but it isapplicable to a sound signal encoder which does not divide an audiosignal into frequency subbands and encode such a residual signal.

Also, the amplitude information encoder and phase information encoderhave been described as separate units, but according to the presentinvention, the they may be constructed to use one to-be-correlatedobject setter and one to-be-correlated selector in common for encodingthe amplitude information and phase information.

Also, the present invention has been described as a hardware, but it isnot limited to the hardware. Any of the operations in the sound signalencoder may be effected by allowing the CPU (central processing unit) toperform a computer program. In this case, the computer program may beprovided via a recording medium having it recorded therein, or bydistribution via an transmission medium such as the Internet.

In the foregoing, the present invention has been described in detailconcerning certain preferred embodiments thereof as examples withreference to the accompanying drawings. However, it should be understoodby those ordinarily skilled in the art that the present invention is notlimited to the embodiments but can be modified in various manners,constructed alternatively or embodied in various other forms withoutdeparting from the scope and spirit thereof as set forth and defined inthe appended claims.

INDUSTRIAL APPLICABILITY

As having been described in the foregoing, the present inventionprovides the sound signal encoding method, in which in encoding soundsignals from a plurality of channels, an arbitrary number of sine wavesare extracted from each of the sound signals from the plurality ofchannels, first-channel information including sine wave informationstanding on a sine wave extracted from a first one of the plurality ofchannels and second-channel information including sine wave informationstanding on a sine wave extracted from a second one of the plurality ofchannels or sine wave information standing on a predetermined sine waveare used to set one of the sine wave information in the second-channelinformation or the sine wave information standing on the predeterminedsine wave as a to-be-correlated object for encoding in correlation witheach sine wave information in the first-channel information, the sinewave information in the second-channel information is encoded and thesine wave information in the first-channel information is encoded usingthe correlation with the sine wave information set as theto-be-correlated object.

By the above sound signal encoding method and the sound signal encodingapparatus adopting the method, in order to encode sine wave informationfrom a first channel can be encoded with an improved efficiency bysetting one of sine wave information from a second channel orpredetermined sine wave information as a to-be-correlated object incorrelation with the first-channel sine wave information, and encodingthe first-channel sine wave information using the correlation with thesine wave information as the to-be-correlated object.

Also the present invention provides the sound signal decoding method andapparatus, in which in restoring sound signals from a plurality ofchannels by decoding a sine wave information code obtained by extractingan arbitrary number of sine waves from each of the sound signals fromthe plurality of channels, using first-channel information includingsine wave information standing on a sine wave extracted from a first oneof the plurality of channels and second-channel information includingsine wave information standing on a sine wave extracted from a secondone of the plurality of channels or sine wave information standing on apredetermined sine wave to set one of the sine wave information in thesecond-channel information or the sine wave information standing on thepredetermined sine wave as a to-be-correlated object for encoding incorrelation with each sine wave information in the first-channelinformation, encoding the sine wave information in the second-channelinformation and encoding the sine wave information in the first-channelinformation using the correlation with the sine wave information set asthe to-be-correlated object, the sine wave information in the encodedsecond-channel information is decoded, the sine wave information in theencoded first-channel information is decoded using the correlation withthe sine wave information set as the to-be-correlated object, and thesound signals from the plurality of channels are restored on the basisof the sine wave information in the first-channel information and sinewave information in the second-channel information.

By the above sound signal decoding method and apparatus, the encodedfirst-channel sine wave information can be decoded using the correlationwith one of the second-channel sine wave information or predeterminedsine wave information and without information indicating any object setat the encoding side, by decoding the encoded second-channel sine waveinformation and then decoding the encoded first-channel sine waveinformation using the correlation with the sine wave information set asthe to-be-correlated object.

Also the present invention provides the sound signal encoding method andapparatus, in which in encoding sound signals from a plurality ofchannels, an arbitrary number of gain control information are generatedcorrespondingly to the amplitude of the sound signals from the pluralityof channels for gain control of the sound signals, the gain controlinformation generated for the first-channel sound signal and gaincontrol information generated for the second-channel sound signal areused to set one of the second-channel gain control information orpredetermined gain control information as an to-be-correlated object forencoding in correlation with each first-channel gain controlinformation, the second-channel gain control information is encoded, andthe first-channel gain control information is encoded using thecorrelation with the gain control information set as theto-be-correlated object.

By the above sound signal encoding method and apparatus, thefirst-channel gain control information can be encoded with an improvedefficiency by setting one of the second-channel gain control informationor predetermined gain control information as the to-be-correlated objectin correlation with the first-channel gain control information, andencoding the first-channel gain control information using thecorrelation with the gain control information as the to-be-correlatedobject.

Also the present invention provides the sound signal decoding method andapparatus, in which in restoring sound signals from a plurality ofchannels by decoding a gain control information code obtained bygenerating an arbitrary number of gain control informationcorrespondingly to the amplitude of the sound signals from the pluralityof channels for gain control of the sound signals, using the gaincontrol information generated for the first-channel sound signal andgain control information generated for the second-channel sound signalto set one of the second-channel gain control information orpredetermined gain control information as an to-be-correlated object forencoding in correlation with each first-channel gain controlinformation, encoding the second-channel gain control information, andencoding the first-channel gain control information using thecorrelation with the gain control information set as theto-be-correlated object, the encoded second-channel gain controlinformation is decoded, the encoded first-channel gain controlinformation is decoded using the correlation with the gain controlinformation set as the to-be-correlated object, and gain controlcorrection is made on the basis of the first-channel information andsecond-channel gain control information.

By the above sound signal decoding method and apparatus, the encodedfirst-channel gain control information can be decoded using thecorrelation with one of the second-channel gain control information orpredetermined gain control information by decoding the encodedsecond-channel gain control information and then decoding the encodedfirst-channel gain control information using the correlation with thegain control information set as the to-be-correlated object.

Also the present invention provides the program allowing a computer toexecute the above sound signal encoding or decoding. Also the presentinvention provides the computer-readable recording medium having theprogram recorded therein.

The above program and recording medium enable implementation of theaforementioned sound signal encoding or decoding by a software

Also the present invention provides the recording medium having a sinewave information code or gain control information code obtained throughthe sound signal encoding.

1. A method of encoding sound signals on a plurality of channels using asound signal encoder, said sound signal encoder comprising a pluralityof sine wave extraction units and a to-be-correlated object setter, saidmethod comprising the steps of: (a) extracting, with the sine waveextraction units, an arbitrary number of sine waves from each of thesound signals on the plurality of channels, said arbitrary number ofsine waves comprising (i) at least a first sine wave extracted from afirst channel, said first sine wave having associated first-channelinformation, and (ii) a second sine wave extracted from a secondchannel, said second sine wave having associated second-channelinformation; and (b) setting a to-be-correlated object, said settingstep comprising (i) determining, with the to-be-correlated objectsetter, an absolute value of a difference between frequency informationincluded in the first-channel information and frequency informationincluded in the second-channel information, (ii) when said difference isless than a threshold, setting, with the to-be-correlated object setter,the second-channel information as the to-be-correlated object forencoding the second-channel information and the first-channelinformation, and (iii) when said difference is not less than thethreshold, setting, with the to-be-correlated object setter, a defaultvalue as the to-be-correlated object for encoding the second-channelinformation and the first-channel information.
 2. The method of claim 1,wherein the to-be-correlated object comprises a default value when thereis no sine wave information in the second one of the plurality ofchannels.
 3. The method of claim 1, wherein the to-be-correlated objectcomprises sine wave information corresponding to a predetermined sinewave when there is no sine wave information in the second channel. 4.The method of claim 3, wherein: the first-channel information comprisesamplitude of the first sine wave, the second-channel informationcomprises amplitude of the second sine wave, the sine wave informationcorresponding to the predetermined sine wave comprises amplitude of thepredetermined sine wave, and encoding the second-channel informationcomprises variable-length coding of a difference between amplitude ofthe to-be-correlated object and amplitude of the first sine wave.
 5. Themethod of claim 3, wherein: the first-channel information comprisesphase of the first sine wave, the second-channel information comprisesphase of the second sine wave, the sine wave information correspondingto the predetermined sine wave comprises phase of the predetermined sinewave, and encoding the second-channel information comprisesvariable-length coding of a difference between phase of theto-be-correlated object and phase of the first sine wave.
 6. The methodof claim 1, wherein encoding the second-channel information comprisesencoding only the first-channel information when all the first-channelinformation coincides with information from a selected one of thesecond-channel information and information corresponding to apredetermined sine wave.
 7. The method of claim 1, wherein encoding thesecond channel information comprises encoding only amplitude informationincluded in the first-channel information when all the amplitudeinformation in the first-channel information coincides with amplitudeinformation from a selected one of the second-channel information andamplitude information corresponding to a predetermined sine wave.
 8. Themethod of claim 1, wherein encoding the second channel informationcomprises encoding only phase information included in the first-channelinformation when all the phase information in the first-channelinformation coincides with amplitude information from a selected one ofthe second-channel information and amplitude information correspondingto a predetermined sine wave.
 9. A sound signal encoder for encodingsound signals from a plurality of channels, the apparatus comprising:(a) a plurality of sine wave extraction units for extracting anarbitrary number of sine waves from each of the sound signals on theplurality of channels, said arbitrary number of sine waves comprising(i) at least a first sine wave extracted from a first channel, saidfirst sine wave having associated first-channel information, and (ii) asecond sine wave extracted from a second channel, said second sine wavehaving associated second-channel information; and (b) a to-be-correlatedobject setter for setting a to-be-correlated object by (i) determiningan absolute value of a difference between frequency information includedin the first-channel information and frequency information included inthe second-channel information, (ii) when said difference is less than athreshold, using the second-channel information as the to-be-correlatedobject for encoding the second-channel information and the first-channelinformation; and (iii) when said difference is not less than thethreshold, using a default value as the to-be-correlated object forencoding the second-channel information and the first-channelinformation.
 10. A computer readable device having recorded therein aprogram for allowing a computer to encode sound signals from a pluralityof channels, the program comprising the steps of: (a) extracting anarbitrary number of sine waves from each of the sound signals on theplurality of channels, said arbitrary number of sine waves comprising(i) at least a first sine wave extracted from a first channel, saidfirst sine wave having associated first-channel information, and (ii) asecond sine wave extracted from a second channel, said second sine wavehaving associated second-channel information; and (b) setting ato-be-correlated object, said setting step comprising (i) determining anabsolute value of a difference between frequency information included inthe first-channel information and frequency information included in thesecond-channel information, (ii) when said difference is less than athreshold, using the second-channel information as the to-be-correlatedobject for encoding the second-channel information and the first-channelinformation, and (iii) when said difference is not less than thethreshold, using a default value as the to-be-correlated object forencoding the second-channel information and the first-channelinformation.
 11. A recording device having recorded therein a string ofcodes generated by a method of encoding sound signals from a pluralityof channels, the string of codes being sine wave information codesobtained by: (a) extracting an arbitrary number of sine waves from eachof the sound signals on the plurality of channels, said arbitrary numberof sine waves comprising: (i) at least a first sine wave extracted froma first channel, said first sine wave having associated first-channelinformation, and (ii) a second sine wave extracted from a secondchannel, said second sine wave having associated second-channelinformation; and (b) setting a to-be-correlated object, said settingstep comprising (i) determining an absolute value of a differencebetween frequency information included in the first-channel informationand frequency information included in the second-channel information,(ii) when said difference is less than a threshold, using thesecond-channel information as the to-be-correlated object for encodingthe second-channel information and the first-channel information, and(iii) when said difference is not less than the threshold, using adefault value as the to-be-correlated object for encoding thesecond-channel information and the first-channel information.
 12. Asound signal decoding method of restoring sound signals from a pluralityof channels, said sound signals having been encoded by (a) extracting anarbitrary number of sine waves from each of the sound signals from theplurality of channels, said arbitrary number of sine waves comprising atleast a first sine wave extracted from a first channel, said first sinewave having associated first-channel information, and a second sine waveextracted from a second channel, said second sine wave having associatedsecond-channel information; and (b) setting a to-be-correlated object,said setting step comprising (i) determining an absolute value of adifference between frequency information included in the first-channelinformation and frequency information included in the second-channelinformation; (ii) when said difference is less than a threshold, usingthe second-channel information as the to-be-correlated object forencoding the second-channel information and the first-channelinformation, and (iii) when said difference is not less than thethreshold, using a default value as the to-be-correlated object forencoding the second-channel information and the first-channelinformation, the method comprising the steps of: decoding, with a sinewave information decoder, the encoded second-channel information anddecoding, with the sine wave information decoder, the encodedfirst-channel information using the to-be-correlated object; andrestoring the sound signals from the plurality of channels on the basisof the first-channel information and the second-channel information. 13.The method of claim 12, wherein the to-be-correlated object comprises adefault value when there is no sine wave information in the second oneof the plurality of channels.
 14. The method of claim 12, wherein theto-be-correlated object comprises sine wave information corresponding toa predetermined sine wave when there is no sine wave information in thesecond channel.
 15. The method of claim 14, wherein: the first-channelinformation comprises amplitude of the first sine wave, thesecond-channel information comprises amplitude of the second sine wave,the sine wave information corresponding to the predetermined sine wavecomprises amplitude of the predetermined sine wave, and encoding thesecond-channel information comprises variable-length coding of adifference between amplitude of the to-be-correlated object andamplitude of the first sine wave.
 16. The method of claim 14, wherein:the first-channel information comprises phase of the first sine wave,the second-channel information comprises phase of the second sine wave,the sine wave information corresponding to the predetermined sine wavecomprises phase of the predetermined sine wave, and encoding thesecond-channel information comprises variable-length coding of adifference between phase of the to-be-correlated object and phase of thefirst sine wave.
 17. The method of claim 12, wherein encoding thesecond-channel information comprises encoding only the first-channelinformation when all the first-channel information coincides withinformation from a selected one of the second-channel information andinformation corresponding to a predetermined sine wave.
 18. The methodof claim 12, wherein encoding the second channel information comprisesencoding only amplitude information included in the first-channelinformation when all the amplitude information in the first-channelinformation coincides with amplitude information from a selected one ofthe second-channel information and amplitude information correspondingto a predetermined sine wave.
 19. The method of claim 12, whereinencoding the second channel information comprises encoding only phaseinformation included in the first-channel information when all the phaseinformation in the first-channel information coincides with amplitudeinformation from a selected one of the second-channel information andamplitude information corresponding to a predetermined sine wave.
 20. Asound signal decoder for restoring sound signals from a plurality ofchannels, said sound signals having been encoded by (a) extracting anarbitrary number of sine waves from each of the sound signals from theplurality of channels, said arbitrary number of sine waves comprising atleast a first sine wave extracted from a first channel, said first sinewave having associated first-channel information, and a second sine waveextracted from a second channel, said second sine wave having associatedsecond-channel information; and (b) setting a to-be-correlated object,said setting step comprising (i) determining an absolute value of adifference between frequency information included in the first-channelinformation and frequency information included in the second-channelinformation; (ii) when said difference is less than a threshold, usingas the to-be-correlated object for encoding the second-channelinformation and the first-channel information, and, (iii) when saiddifference is not less than the threshold, using a default value as theto-be-correlated object for encoding the second-channel information andthe first-channel information, the apparatus comprising: a sine waveinformation decoder configured to decode the encoded second-channelinformation and decoding the encoded first-channel information using theto-be-correlated object; and a sound signal restorer configured torestore the sound signals from the plurality of channels on the basis ofthe first-channel information and the second-channel information.
 21. Acomputer-readable recording device having recorded therein a program forallowing a computer to decode sound signals from a plurality ofchannels, said sound signals having been encoded by (a) extracting anarbitrary number of sine waves from each of the sound signals from theplurality of channels, said arbitrary number of sine waves comprising atleast a first sine wave extracted from a first channel, said first sinewave having associated first-channel information, and a second sine waveextracted from a second channel, said second sine wave having associatedsecond-channel information; and (b) setting a to-be-correlated object,said setting step comprising (i) determining an absolute value of adifference between frequency information included in the first-channelinformation and frequency information included in the second-channelinformation; (ii) when said difference is less than a threshold, usingthe second-channel information as the to-be-correlated object forencoding the second-channel information and the first-channelinformation, and (iii) when said difference is not less than thethreshold, using a default value as the to-be-correlated object forencoding the second-channel information and in the first-channelinformation, the program comprising the steps of: decoding the encodedsecond-channel information and decoding the encoded first-channelinformation using the to-be-correlated object; and restoring the soundsignals from the plurality of channels on the basis of the first-channelinformation and the second-channel information.